Lamp socket for series lighting circuits



Oct. 1l, 1949. M. c. wALTz LAMP SOCKET FOR SERIES LIGHTING CIRCUITSFiled Sept. 27, 1947 /N VEA/TOR M. C .W4 L TZ Patented Oct. 11, Y1949'ffUNTED,,STATE Maynard o. Wal-tz,

Maplewood, assigner-tto Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New Yorkv r v Application This inventionvrelates to lamp sockets and more particularly to sockets for use inseries-lighting circuits.

The object of thisinventionis to automatically shunt an inoperativeseries-connectedlamp on thefailure of said lamp. ,ff'Heretofore numerousmeans have been vSuggested and, employed to maintain the operation of aseries-lighting circuit, notwithstanding a failure of one or more of thelamps. Broadly classed, these means have included mechanical shunts bothautomatically and manually operated, and electrical shunts operated bythe rupturing of an insulating lm, by placing a high resistance acrossthe lower resistance of the filament, or by connecting a semiconductorhaving a negative temperature coefficient of resistance across the lamp.

In accordance with this invention an improved structure is provided forshunting a series-connected lamp which has failed by utilizing amaterial having a negative temperature coefficient oi resistance andassociating it with a shell for a socket in a manner such that a verysatisfactory lamp socket is realized which is compact, simple and easilymanufactured.

More particularly this invention comprises a lamp socket for aseries-lighting circuit, for example, a series-lighting circuit for aChristmas tree, having a centrally apertured disc of material having anegative coeiiicient of resistance secured in the bottom of the shellforming a mechanical support for the lamp. The central contact of thelamp passes through a central aperture in the disc thereby permanentlyshunting the disc across the lamp lament.

The various features of this invention will be better understood fromthe following detailed description when considered in conjunction withthe accompanying drawings in which:

Fig. 1 discloses in the main a sectional view of a socket illustrativeof one embodiment of this invention, and

Fig. 2 is a detailed plan View of the socket of Fig. 1.

The drawings show a lamp socket of the conventional typev having anouter casing I of insulating material in which a threaded shell contactI I containing a central contact I2 is suitably secured. Leads I3 and I4are connected to the shell contact Il and the central contact I2,respectively, to complete the circuit from the source through the leadsI3 and I4, the contacts II and I2 and a lamp L mounted in the socket.Secured within the bottom of the shell contact II in a September 27,1947; Serial No. 775,697 J3 cisnes.- 01; 2er-449i suitable manner, suchas by spinning or lcrimpin in its lower edge 'I5 is a centrallyapertured disc I6 of a material having a high negative tempera@ turecoefficient of resistance. A suitable material for this disc is thatdisclosed in Patent 2,258; l(546 to Grisclale of October 14, 1941. Thisdisc .I6 structurally replaces the nber or ceramic insulating-ldiscwhich is usuallymounted inthe shell contact of an ordinary socket tosupport the central contact, and simultaneously provides a shunt betweenthe shell contact II and the central contact I2 across the filament ofthe lamp. In order to insure adequate electrical contacts havingconstant resistances between the shell contact Il and the disc I6 andbetween the central contact I2 and the disc I6 the outer and innerperipheries have coverings or electrodes I1 and I8 (shown with anexaggerated thickness for purposes of clarity) deposited thereon, thusproviding metal-to-metal contacts between these members.

This socket may be employed in a series circuit. for example, aChristmas tree lighting circuit having a plurality of lamps. W'henconnected in a circuit of this nature with an operative lamp secured inthe socket, the resistance of the material of the disc I6 is such thatthe resistance between the contact II and the contact I2 across the discis, relative t0 the lamp lament, effectively an open circuit, and thedisc performs only the mechanical function of supporting the centralcontact I2. However on rupture of the circuit through the lamp anincreased electromotive force is impressed across the disc causing anincrease in the normally minute current flowing therethrough. Theincreased current flow increases the rate of heat generation within thedisc such that it ls greater than the heat dissipated and thus thethermal unbalance causes an increase in the temperature and acorresponding decrease of the resistance of the disc to a point limitedby the resistance of the circuit where the resistance of the disc againstabilizes. This second stable resistance value is approximately equalto the resistance of the parallel lamp and disc which it has replaced,thus restoring the normal operation of the remainder of the circuit, thevalue being determined in the well-known manner by the selection of amaterial having the desired negative temperature coeflicient ofresistance and a structure having the desired thermal, electrical andmechanical characteristics.

As many possible embodiments may be made of the above invention and asmany changes might be made in the embodiment above set forth, it is tobe understood that all matter herelnbefore set forth, or shown in theaccompanying draW- ings, is to be interpreted as illustrative and not ina limiting sense.

What is claimed is:

1. A lamp socket Comprising an electrically conductive shell having twoyopen= ends, the opening in one of said ends being smaller than theopening in the other of said ends, a disc of resistance material havinga negative temperature coem cient of resistance inalterablyv secured inthe,

smaller opening of said shell, said disc havingan aperture at itscenter, a contact in said aperture,

and separate metallic coatings on. the-aperture a contact member spacedfrom said shell, a shunt connected between said shell and said contact,said shunt comprising a disc of material having a high negativetemperature coetlicient of resis tance permanently secured in an end ofsaid shell and supporting said contact member in spaced relationship tosaid shellseparate metallic coatings on said disc engagingsaidzcontactand said shell respectively, and a pair of leading-inconductors for supplying energy to said socket, one

conductor being connected to said shell and the other conductor beingxedly and directly connected to said contact member.

MAYNARD C. WALTZ.

REFERENCES CITED The following references are of record in the meof'this patent:

UNITED. STATES PATENTS Number Name Dots 1,536,332 Dam May, ma 1,641,564Zierdt Sept; 6, 1927 1,941,984 Gustin. et al 1. Jan. 2, 1934 1,950,028Gustin .Mar.,6', 1934 1,954,355 Handy: Apr. 10, 1934 2,258,646 Grisdale.Oct. 14, 1941

